In a game of pool, a 0.4 kg cue ball is traveling at +0.80 m/s when it hits a slower striped ball moving at +0.38 m/s. after the collision, the striped ball moves off at +0.62 m/s.

what is the magnitude of the final velocity of the cue ball? assume all pool balls have the same mass.

The momentum of a certain body is calculated by multiplying its mass and the velocity. In this case,
                              mv1 + MV1 = mv2 + MV2
Since, m (the mass of the cue ball) and M (the mass of striped ball) can be assumed to be the same, they can be erased from the equation. 
                    0.80 m/s + 0.38 m/s = 0.62 m/s + V2
The value of V2 from the equation is 0.56 m/s. 

I’m good with pshycology